Exploring java.lang

Student Name: Student ID:Student Name: Student ID:

Vikethozo Tsira DC2012MCA0006Vikethozo Tsira DC2012MCA0006

Sonnet Debbarma DC2012MCA0007Sonnet Debbarma DC2012MCA0007

Biswajit Thakuria DC2012MCA0019Biswajit Thakuria DC2012MCA0019

L. Chameikho DC2012MCA0020L. Chameikho DC2012MCA0020

Simple Type WrappersSimple Type Wrappers

L ChameikhoL Chameikho

DC2012MCA0020DC2012MCA0020

java.lang is automatically imported into all java.lang is automatically imported into all programs.programs.

java.lang includes the following classes:java.lang includes the following classes:

Primitive Type WrappersPrimitive Type Wrappers

Java uses primitive types, such as int and Java uses primitive types, such as int and char.char.

Primitive types are not part of the object Primitive types are not part of the object hierarchy, and they do not inherit Object.hierarchy, and they do not inherit Object.

Java provides type wrappers, which are Java provides type wrappers, which are classes that encapsulate a primitive type classes that encapsulate a primitive type within an object.within an object.

The type wrappers are Double, Float, Long, The type wrappers are Double, Float, Long, Integer, Short, Byte, Character, and Boolean.Integer, Short, Byte, Character, and Boolean.

Creating an object representation for one of Creating an object representation for one of these primitive types.these primitive types.

Java provides classes that encapsulate, or Java provides classes that encapsulate, or wrap, the primitive types within a class.wrap, the primitive types within a class.

Referred to as type wrappers.Referred to as type wrappers.

Wrapper Classes ConstructorsWrapper Classes Constructors

short or StringShortshort

long or StringLonglong

int or StringIntegerint

float, double, or StringFloatfloat

double or StringDoubledouble

charCharacterchar

byte of StringBytebyte

boolean or String or nullBooleanboolean

Constructor ArgumentsWrapper ClassPrimitive

The Integer and Long classes also provide the The Integer and Long classes also provide the methods toBinaryString( ), toHexString( ), and methods toBinaryString( ), toHexString( ), and toOctalString( ) which convert a value into a toOctalString( ) which convert a value into a binary, hexadecimal, or octal string.binary, hexadecimal, or octal string.

/* Convert an integer into binary, hexadecimal,/* Convert an integer into binary, hexadecimal,and octal.and octal.*/*/

class StringConversions {class StringConversions {public static void main(String args[]) {public static void main(String args[]) {

int num = 19648;int num = 19648;System.out.println(num + " in binary: " +System.out.println(num + " in binary: " +Integer.toBinaryString(num));Integer.toBinaryString(num));System.out.println(num + " in octal: " +System.out.println(num + " in octal: " +Integer.toOctalString(num));Integer.toOctalString(num));System.out.println(num + " in hexadecimal: " System.out.println(num + " in hexadecimal: "

+ Integer.toHexString(num));+ Integer.toHexString(num));}}

}}

Output:Output:

19648 in binary: 10011001100000019648 in binary: 100110011000000

19648 in octal: 4630019648 in octal: 46300

19648 in hexadecimal: 4cc019648 in hexadecimal: 4cc0

System ClassSystem Class

Biswajit ThakuriaBiswajit Thakuria

DC2012MCA0019DC2012MCA0019

System classSystem class

The The java.lang.Systemjava.lang.System class contains several useful class contains several useful class fields and methods. It cannot be instantiated.class fields and methods. It cannot be instantiated.

FACILITIES PROVIDED BY SYSTEM CLASSFACILITIES PROVIDED BY SYSTEM CLASS

Standard outputStandard output Error output streamsError output streams Standard input and access to externally defined Standard input and access to externally defined

properties and environment variables.properties and environment variables. A utility method for quickly copying a portion of an array.A utility method for quickly copying a portion of an array. A means of loading files and librariesA means of loading files and libraries

CLASS DECLARATIONCLASS DECLARATION

Following is the declaration for Following is the declaration for java.lang.Systemjava.lang.System class: class: public final class Systempublic final class Systemextends Objectextends Object  FIELDFIELDFollowing are the fields for Following are the fields for java.lang.Systemjava.lang.System class: class:

static PrintStream err static PrintStream err -- This is the "standard" error output -- This is the "standard" error output stream.stream.static InputStream in static InputStream in -- This is the "standard" input stream.-- This is the "standard" input stream.static PrintStream out static PrintStream out -- This is the "standard" output -- This is the "standard" output stream.stream.

System Class methodsSystem Class methods

SAMPLE PROGRAMSAMPLE PROGRAM

import java.lang.*;import java.lang.*;

public class SystemDemo { public class SystemDemo {

public static void main(String[] args) {public static void main(String[] args) {

int arr1[] = { 0, 1, 2, 3, 4, 5 };int arr1[] = { 0, 1, 2, 3, 4, 5 };

int arr2[] = { 0, 10, 20, 30, 40, 50 };int arr2[] = { 0, 10, 20, 30, 40, 50 };

int i;int i;

// copies an array from the specified source array// copies an array from the specified source array

System.arraycopy(arr1, 0, arr2, 0, 1);System.arraycopy(arr1, 0, arr2, 0, 1);

System.out.print("array2 = ");System.out.print("array2 = ");

System.out.print(arr2[0] + " "); System.out.print(arr2[0] + " ");

System.out.print(arr2[1] + " "); System.out.print(arr2[1] + " ");

System.out.println(arr2[2] + " ");System.out.println(arr2[2] + " ");

for(i = 0;i < 3;i++) for(i = 0;i < 3;i++)

{{ If(arr2[i] > = 20) If(arr2[i] > = 20) { { System.out.println("exit..."); System.out.println("exit...");

System.exit(0); System.exit(0); } } else { else { System.out.println("arr2["+i+"] = " + arr2[i]); System.out.println("arr2["+i+"] = " + arr2[i]); } } } } } }}}

OUTPUTOUTPUT

array2 = 0 10 20 array2 = 0 10 20

arr2[0] = 0 arr2[0] = 0

arr2[1] = 10 arr2[1] = 10

Class classClass class

Vikethozo TsiraVikethozo Tsira

DC2012MCA0006DC2012MCA0006

ClassClass

Class encapsulates the run-time state of an Class encapsulates the run-time state of an object or interfaceobject or interface

Objects of type Class are created automatically, Objects of type Class are created automatically, when classes are loaded.when classes are loaded.

We cannot explicitly declare a Class object.We cannot explicitly declare a Class object.

Class object can be obtained by calling the Class object can be obtained by calling the getClass( ) method defined by Object.getClass( ) method defined by Object.

Class is a generic type:Class is a generic type:

class Class<T>class Class<T>

T is the type of the class or interface represented.T is the type of the class or interface represented.

Methods defined byMethods defined by Class Class

// Demonstrate Run-Time Type Information.// Demonstrate Run-Time Type Information.

class X {class X {

int a;int a;

float b;float b;

}}

class Y extends X {class Y extends X {

double c;double c;

}}

class RTTI {class RTTI {

public static void main(String args[]) {public static void main(String args[]) {

X x = new X();X x = new X();

Y y = new Y();Y y = new Y();

Class<?> clObj;Class<?> clObj;

clObj = x.getClass(); // get Class referenceclObj = x.getClass(); // get Class reference

System.out.println("x is object of type: " +System.out.println("x is object of type: " +

clObj.getName());clObj.getName());

clObj = y.getClass(); // get Class referenceclObj = y.getClass(); // get Class reference

System.out.println("y is object of type: " + System.out.println("y is object of type: " + clObj.getName()); clObj.getName());

clObj = clObj.getSuperclass();clObj = clObj.getSuperclass();System.out.println("y's superclass is " +System.out.println("y's superclass is " +

clObj.getName());clObj.getName());}}

}}

Output:Output:

x is object of type: Xx is object of type: Xy is object of type: Yy is object of type: Yy’s superclass is Xy’s superclass is X

Maths functionsMaths functions

Sonnet DebbarmaSonnet Debbarma

DC2012MCA0007DC2012MCA0007

MathMath The The java.lang.Mathjava.lang.Math class contains methods for  class contains methods for

performing basic numeric operations such as the performing basic numeric operations such as the elementary exponential, logarithm, square root, and elementary exponential, logarithm, square root, and trigonometric functions.trigonometric functions.

Class declarationClass declaration Following is the declaration for Following is the declaration for java.lang.Mathjava.lang.Math class: class:

public final class Mathpublic final class Math

extends Objectextends Object

FieldField

Following are the fields for Following are the fields for java.lang.Mathjava.lang.Math class: class:static double E static double E -- This is the double value that is closer -- This is the double value that is closer than any other to e, the base of the natural logarithms.than any other to e, the base of the natural logarithms.static double PI static double PI -- This is the double value that is closer -- This is the double value that is closer than any other to pi, the ratio of the circumference of a than any other to pi, the ratio of the circumference of a circle to its diameter.circle to its diameter.

  The standard Math library. For the methods in this Class, The standard Math library. For the methods in this Class, error handling for out-of-range or immeasurable results are error handling for out-of-range or immeasurable results are platform dependent. platform dependent. This class cannot be subclassed or instantiated because all This class cannot be subclassed or instantiated because all methods and variables are static.methods and variables are static.  

Math functionsMath functions acosacos(double)(double) Returns the arc cosine of a, in the range of 0.0 through Pi.Returns the arc cosine of a, in the range of 0.0 through Pi. asinasin(double)(double) Returns the arc sine of a, in the range of -Pi/2 through Pi/2.Returns the arc sine of a, in the range of -Pi/2 through Pi/2. atanatan(double)(double) Returns the arc tangent of a, in the range of -Pi/2 through Pi/2.Returns the arc tangent of a, in the range of -Pi/2 through Pi/2. coscos(double)(double) Returns the trigonometric cosine of an angle.Returns the trigonometric cosine of an angle.

Math functionsMath functions powpow(double, double)(double, double) Returns the number a raised to the power of b.Returns the number a raised to the power of b. roundround(float)(float) Rounds off a float value by first adding 0.5 to it and then returning Rounds off a float value by first adding 0.5 to it and then returning

the largest integer that is less than or equal to this new value.the largest integer that is less than or equal to this new value. sinsin(double)(double) Returns the trigonometric sine of an angle.Returns the trigonometric sine of an angle. sqrtsqrt(double)(double) Returns the square root of a.Returns the square root of a. tantan(double)(double) Returns the trigonometric tangent of an angle.Returns the trigonometric tangent of an angle.

// Demonstrate toDegrees() and toRadians().// Demonstrate toDegrees() and toRadians().

class Angles {class Angles {public static void main(String args[]) {public static void main(String args[]) {

double theta = 120.0;double theta = 120.0;System.out.println(theta + " degrees is " +System.out.println(theta + " degrees is " +

Math.toRadians(theta) + " Math.toRadians(theta) + " radians.");radians.");

theta = 1.312;theta = 1.312;System.out.println(theta + " radians is " +System.out.println(theta + " radians is " +

Math.toDegrees(theta) + " Math.toDegrees(theta) + " degrees.");degrees.");}}

}}

Output:Output:

120.0 degrees is 2.0943951023931953 radians.120.0 degrees is 2.0943951023931953 radians.

1.312 radians is 75.17206272116401 degrees.1.312 radians is 75.17206272116401 degrees.